Fortress Press have just released a new book edited by Mark Nanos and Magnus Zetterholm: Paul within Judaism. Taking the "New Perspective on Paul" a step further, this is a collection of essays/chapters by scholars who are trying to see Paul (Rav Sha'ul to you and me) staying within the Judaism that he knew.

In the chapter by Caroline Johnson Hodge, "The Question of Identity: Gentiles as Gentiles - but also Not - in Pauline Communities", the author speaks about the difference between these Gentiles and those Gentiles. Then she makes this claim:

As I have discussed at length elsewhere, baptism in Paul is a ritual of adoption, creating a kinship relationship between gentiles and Abraham (Gal 3, Rom 4).